1. Field of the Invention
This invention is directed to a belt conveyor system, and in particular to a conveyor system incorporating pneumatic transfer.
2. Description of the Prior Art
Belt conveyors for transferring articles are widely used in industry, including incorporation as integral parts of production lines, for a wide range of products,. Such production lines frequently have work stations at spaced intervals, at which the conveyor is required to stop, to enable working upon the conveyed article. In such instances the precise monitoring of the displacement of the conveyor belt along its path becomes very important. Present systems, which monitor travel of the conveyor belt for such location purposes by encoding the revolutions of the driving motor, suffer from inaccuracy, due to belt slippage which generates discrepancies between rotation of the driving motor and the actual travel of the belt. Inconsistencies in belt tension, with consequent variations in the rates of belt slippage, exacerbate this problem.
Certain types of article, for example lightweight articles having relatively large surface areas, such as plastic sheets, sheets of thin metal, cardboards, including cardboard blanks and blocks generally have smooth, low friction surfaces that make their transfer and handling most difficult. In some instances, such problems are accentuated, due to the relative fragility of the articles, or other factors such as a susceptibility to becoming marked on their surfaces, as a consequence of transfer to or passage along a conveyor, including encounter with hard stops and position sensing mechanical feelers.
The use of pneumatic transfer with conveyor systems is well known, and widely practiced, both in regard to belt conveyors and for agricultural purposes, such as the blowing of grain along pipes.
In the case of belt conveyors with pneumatic transfer many existing systems are characterized by their use of wide-area suction chambers, with associated unduly large air-mass displacement requirements, in the form of generated vacuum, or of compressed air. The response times of such systems is unduly slow, while the necessary air displacement is large, and excessive forces may be generated against system components, including the associated friction drag upon the belt. In other systems, the large size of certain vacuum system components necessitates unduly large belt turning radii, with correspondingly large end pulleys and related space requirements.
It should be noted that the size of a conveyor system per se, both in height and width, can bear significant economic implications, with down-sizing being most desireable. This has particular bearing on the size and location of the necessary anciliary systems associated with the conveyor. The driving systems for conveyors usually employ a chain or other transmission acting upon the end roller of the conveyor, usually at the oncoming end. Certain disadvantages associated with these earlier arrangements include unsatisfactory frictional tractive effort between the pulley and the belt, due to the limited (180 degree or less) wrap of the belt on the pulley, and shortage of space at the conveyor end, where the motor and reduction gear are located. Also, this system limits and complicates the belt tensioning arrangements, as tractive transfer at the pulley is dependent upon the extent of belt wrap about the pulley, and belt tension.
Inadequate belt tensioning also results in excessive lost motion when the drive is reversed, in order to reverse the conveyor. This exacerbates the problems encountered in achieving accurate registry of the conveyor with the associated workstations.
The handling of ferritic sheet metal production lines has involved magnetic conveyors, which employ magnets to secure the sheet to the conveyor. There is a requirement to handle sheets of different thickness, and to permit precise manipulation of them for purposes such as the welding together of two adjoining sheets of different thickness, to form welded blanks for automotive stampings, for which operations the characteristics of magnetic attachment are not well suited. Magnetic conveyors are also ineffective for handling aluminum or stainless steel sheet.
The present invention provides a modular pneumatic transfer system for conveyors, the conveyor system consisting of a plurality of individual transfer blocks, over which a perforated conveyor belt runs.
The aligned transfer blocks occupy the top of a beam that extends the length of the conveyor. The subject modular system incorporates a transfer suction block for operation with a belt conveyor, the system incorporating an air driven, reaction sensing means to determine the presence of an article upon the conveyor above the block; air-driven vacuum generation means; and a pneumatic control actuated by the sensing means to operate the vacuum generation means, to apply vacuum by way of the suction block, through the perforated belt to the over-lying section of the conveyor, in response to the sensed presence of an object upon that section of the conveyor.
The vacuum generation means consists of a multi-stage air-driven venturi, having a high pressure air jet or jets discharging through convergent-divergent nozzles, serving as an air ejector, to thereby provide a source of high volume air flow, generating a correspondingly rapid rate of high vacuum, which is applied to the suction block of a module.
In one embodiment, each module may have its respective vacuum generator. However, it will be understood that a larger vacuum generator may be used to service a number of modules, the respective object-sensing sensors being used to switch the vacuum to the related module.
The reaction sensing means consists of low pressure air jet means having an escape flow path immediately adjacent an edge of the conveyor belt, the partial blocking of which flow path by the presence of an overlying object causes a build-up in back-pressure in the air supply circuit of the sensor, sufficient to actuate an air servo-valve, thereby admitting supply air to the air displacement (vacuum generation) means. This action causes rapid displacement of air from the transfer block, and applies suction to the block, which suction is transferred through the perforated belt to the overlying object, causing it to be drawn down to the belt, and transferred.
In the preferred system embodiment the subject suction blocks are each part of an individual module, each module being essentially self contained, with its own sensing means and associated air displacement unit. This enables the provision of exceedingly compact system elements, the modular nature of which enable the provision of conveyors of virtually any desired length.
The suction blocks are selectively located to provide a desired presence-sensing and air displacement pattern in conjunction with the adjoining, superposed perforated conveyor belt. In the preferred embodiment the low pressure sensing jet forms a part of the suction block. However it will be understood that this is not imperatively the case, as the sensor may be physically located independent of the suction block.
The suction blocks are of generally small size, being made of hardened, Teflon (T.M.) coated a aluminum, or of plastic or ceramic, and being further characterized by having a shallow top groove for passage of a conveyor belt therealong. The belt fits closely in the groove, the groove sides serving to guide the belt in its passage along the beam, and to complement the sealing of the belt to the block with substantially no increase in wear or drag upon the belt or the block.
The conveyor has a series of the subject suction blocks mounted in mutual, substantially end-to-end relation upon a hollow beam extending the length of the conveyor, portions of the beam interior serving as air passages for the conveyor air system.
In operation, a respective suction block only comes into operation when the belt portion passing over that block is carrying something that obstructs the sensor so as to actuate the air servo, thus energizing the air transfer means, which in this case operate as vacuum generation means, thereby applying suction to the associated block.
The surface of the suction block has discrete, longitudinally extending air-way grooves positioned laterally directly below the longitudinal axis along which the vertical apertures of the belt are located. This directs the suction applied to the block directly to the belt apertures, and thus minimizes the suction force acting upon the belt, per se; while also minimizing the interior air space, and the mass air displacement required to effect vacuum at the belt upper surface.
The block module thus provides an extremely rapid suction response to operation of the sensor, with correspondingly rapid operation of the air transfer means
Accordingly, it will be appreciated that the reaction forces generated between the belt and the suction block consist normally of only the load applied by the belt and its superimposed load; and that the addition of suction forces acting upon the belt occurs only when the sensor of a selected block is activated by the presence of a superimposed load object upon the belt, whereby the respective individual block system is energized, and suction is applied to the block, causing draw-down to the belt of the overlying object. Thus, the major reactive forces brought into play by operation of the block under vacuum, are between the belt upper surface and the overlying object. In this way, the gross frictional drag between the block and the belt is minimized.
The system includes a novel belt drive arrangement. This includes an electric drive motor driving a reduction gear, the output of which is transferred by a toothed belt to the conveyor belt driving pulley. A pair of guide pulleys on opposite sides of the drive pulley provide a deep, variable draw of the conveyor belt about the drive pulley, by controlling the extent of belt wrap about the drive pulley. The variable one of the guide pulleys can also be adjusted to control the pressure of the conveyor belt against the surface of the drive pulley, which may be rubber-coated. The variable guide pulley may have an adjustable loading spring, to promote consistent conveyor belt tension and drive-pulley contact pressure, and may include a pulley position indicator.
The conveyor belt drive and tensioning unit, which operates on the return run of the conveyor belt, is preferably located intermediate the ends of the conveyor section, thus enabling the use of smaller conveyor end rolls, while locating the belt drive in a more accessible location.
A particular advantage of this arrangement is that conveyor belt backlash is virtually eliminated, so that in the event of reversing the conveyor there is no lost motion, due to belt slack and/or gear back-lash. This facilitates accurate xe2x80x9cstation-keepingxe2x80x9d in relation to adjusting and maintaining the stopping and starting of the conveyor in step with the work stations, by the operation of the location encoder.
In the present invention the encoder is driven off the conveyor belt end pulley, in contrast to the prior art systems that have the location encoder driven off the electric drive motor, as discussed above.
The conveyor drive includes a foot bracket, and side brackets that are attached to the sides of, and support the conveyor beam, such that one end of the conveyor is supported on the foot bracket, by means of which the conveyor may be secured to the floor, or from a framework.
The conveyor drive may consist of a central motor driving a number of conveyors by way of a transversely extending splined shaft, thus providing a flexible arrangement for the lateral repositioning of the respective conveyors along the length of the shaft.
In such an arrangement, each conveyor drive is connected to the splined shaft through a clutch, which allows conveyors to be shut off when not needed.
The modular suction blocks can also be utilized as blower blocks, wherein, upon the sensing of an object above the block, the servo-valve admits air to the block at a predetermined pressure above atmospheric, to serve as a supporting air cushion for the sensed object. One example of this aspect of the modular block might be a conveyor system having a pair of spaced outer belts running on xe2x80x9cvacuumxe2x80x9d for the transfer of objects such as large steel sheets, wherein the system includes a number of modular xe2x80x9cpressurexe2x80x9d blocks located intermediately of the two outer belts, being equipped with the air sensor, and being supplied with air under pressure, in the presence of a sensed load, and serving as air-cushion blocks, over which the load rides.
The upper surface of these blocks would be substantially level with the top surface of the two outer belts, such that, upon the approach of a transported sheet, the outer suction blocks associated with the two conveyor belts would be actuated to apply suction to the overlying sheet, to hold it to the conveyor belts. Meanwhile, the intermediate blower blocks would serve as support slippers, over which the transported sheet would ride upon the individual air cushions of the respective blower blocks.
Owing to the individual sensing jets of both the suction and the blower block modules, air consumption is minimized, as air pressure is applied to each of the multi-stage vacuum-creating ejectors and to each blow block only when the presence of the transported sheet is sensed in the immediate vicinity of the respective block.
On passage of the sheet beyond any one of the respective blocks, the respective high pressure or ejector air supply is terminated. Thus, highly efficient utilization of air is achieved.